A conventional photosensitive resin is classified as a positive type in which an exposed part is dissolved or as a negative type in which an exposed part is cured and remains during development. The positive photosensitive resin may in general be synthesized by using polybenzoxazole having a phenol-based hydroxy group dissolved in an alkali an aqueous solution and the like.
The polybenzoxazole is a polymer having a rigid aromatic backbone. Polybenzoxazole can have excellent mechanical strength, chemical resistance, weather resistance, heat resistance, and/or shape stability based on cyclic chemical stability as well as excellent electric characteristics such as insulation properties and the like due to a low dielectric constant. Thus, polybenzoxazole is actively used in the manufacture of electric/electronic materials such as a display, a memory, a solar cell, and the like. Polybenzoxazole has also drawn attention as a material for use in automotive and aerospace fields.
In particular, positive photosensitive resin compositions including polybenzoxazole are increasingly used in the display area as an organic insulation layer or a barrier rib material and has been extensively used for a laptop computer, a monitor, and a TV image due to lightness, thinness, low price, and low power consumption of a display, excellent adherence to an integrated circuit, and the like. However, a polybenzoxazole precursor (a polybenzoxazole polymer, PBO) may not form a pattern with high resolution due to low solubility for an alkali developing solution and lack of a large dissolution rate difference between exposed and non-exposed parts.
A photosensitizer suppressing dissolution of a resin during non-exposure and stopping the dissolution suppression during exposure may be mixed with the resin to effectively form the pattern. The mixture, however, may not be uniformly coated and can still form a non-uniform pattern during development.
Accordingly, there is a need for a resin having selectively increased solubility for an alkali developing solution in an exposed part.